Prosecution authorities are reviewing their move to extradite the parents of Ashya King, the five-year-old cancer patient in hospital in Spain after he was taken from hospital in Southampton. Meanwhile, the government has contacted police and health officials to see whether Ashya can be reunited with his mother and father.

The new interventions follow mounting calls for Brett and Naghmeh King, held in separate prisons near Madrid, to be brought to Málaga, where Ashya is being cared for at a children's hospital. The couple had taken the boy from Southampton general hospital without doctors' consent and say they want alternative treatment abroad for his brain tumour.

David Cameron's spokesman said the Home Office had been in touch with Hampshire police force over the case, while the Department of Health contacted Southampton hospital. The hospital first raised the alarm on Thursday after Ashya was taken away.

Downing Street stressed the need for judicial authorities to be able to operate independently of politicians, but it is clear that Cameron shares the concerns expressed by Nick Clegg that the handling of the case has been heavy-handed.

Earlier on Tuesday the deputy prime minister questioned why the "full force of the law" was being used against the parents and called for the family to be reunited.

Separately, Labour MP Kate Hoey asked the Home Secretary, Theresa May, in the Commons about the handling of the case. May replied: "I hope the lady will be reassured that the CPS are reviewing this issue as we speak."

A CPS spokeswoman confirmed the matter was being reassessed, saying: "Further evidence is now being provided to the CPS and so the case is under immediate review."

The Kings hope to take Ashya to the Czech Republic to undergo proton beam therapy for the tumour. The treatment, not routinely available in Britain, is a form of radiotherapy that does less damage to healthy tissue compared with conventional x-ray-based treatments.

Their removal of the boy, against medical advice, prompted Southampton general hospital to ask the local council, Portsmouth, to apply for temporary wardship of Ashya, while Hampshire police sought a European arrest warrant via the CPS on the basis that the parents' actions amounted to possible cruelty against a minor.

On Tuesday, the leader of Portsmouth city council urged the CPS to drop extradition proceedings and "resolve this distressing situation".

Donna Jones said: "Like others who have been watching this upsetting case unfolding in the media, I have been moved by the plight of the King family and am most concerned about Ashya. I believe what he needs now is to be with his family.

"That's why I am urging the CPS to urgently review the case involving Ashya King's parents and remove any extradition proceedings, so the family can be reunited with their five-year-old son."

A hearing is taking place at the high court in London on Tuesday afternoon to review the council's temporary wardship of the boy.

For now the parents remain in jails in Madrid, after a Spanish judge ruled they be remanded for up to 72 hours while the court considers whether to grant a British extradition request, which the parents are resisting. Ashya's condition is said to be stable in Málaga.

Juan Isidro Fernandez Diaz, the couple's lawyer in Spain, said they were considering suing the NHS. He told BBC Radio 5 Live: "They are going to prepare legal demands against the hospital in Southampton. Legal action will be against the hospital."

"A little boy is on his own in a hospital, doesn't speak Spanish, is cut off from his parents and his siblings and I would like to see him together with his family as soon as possible," Clegg told BBC Breakfast.

Clegg said: "My heart goes out, and I'm sure every mum or dad will have the same response, which is, as far as I can make out, this is a family in a state of real anguish who have taken this exceptional step of moving their sick child to another country because they think that's what is best for their child.

"We can debate whether it is or is not but that seems to be their motive and those are not motives I can argue with.

"That's why I personally think that throwing the full force of the law at Mr and Mrs King, who appear to be doing what they believe to be best for their own family, I don't think is an appropriate thing to do. But that, at the end of the day, is for the police and the CPS and others to decide."

The London mayor, Boris Johnson, said on LBC radio: "It seems pretty obvious to me that the parents and the suffering child should be united and if they've got a plan to help cure their boy's illness then they should be supported in that. I've probably gone as far I can go, it sounds potty to me, frankly, but I don't know the details of the case.

"Every person's instinct will be that the parents have care of the child. Somebody's going to have to do some very, very lengthy explaining about what the hell went on here."

The comments came amid signs of a rethink by British authorities about how the Kings' case was handled.

The Kings took Ashya from the hospital on Thursday and travelled to France with him and his six siblings before heading to the Costa del Sol in southern Spain. Brett, 51, and Naghmeh, 45, were arrested in Velez-Málaga on Saturday night.

The couple say they hope to sell an apartment they own near Málaga to raise funds for the proton beam therapy.